•23'2 PRINCIPLES OF GARDEXINO. [CH. VII. 



being thirty feet long, five pipes of that length, and 

 five inches in diameter, will be about the proper 

 quantity. 



If hot water be employed instead of steam, the 

 following proportions and information, ol>tained from 

 Mr. Rendle, may be adopted confidently as guides. 

 In a span roof propagating house forty feet long, 

 thirteen feet broad, seven feet high in the centre, 

 and four feet high at the two fronts, having a super- 

 ficial surface of glass amounting to 538 square feet, 

 Mr. Rendle has a tank eighty-three feet long, 

 running round three sides of the house, four feet 

 mde and about eight inches deep, and consequently 

 capable of containing nearly 300 cubic feet of hot 

 water, though only half that quantity is used. This 

 is closely approaching to the size pointed out accord- 

 ing to Mr. Tredgold's formida. The mean tem- 

 perature of a hot water tank will never be much 

 above 160 \ so that for the sized house mentioned by 

 that slvilful engineer, the divisor must be '2.1 times 

 the diff"erence between 160' and 60", which gives as 

 the quotient 335 cubic feet. 



The tank in Mr. Rendle s propagating house is 

 built of bricks lined ^vith Roman cement, and if the 

 temperature at the time of lighting the fire be 90", 

 the temperature of the atmosphere of the house 67°, 

 and the temperature out of doors 50°, the quantity 

 of small coal, or breeze, required to raise the tern- 



